1. Field of the Invention
The present invention relates to a power supply controller apparatus for use in a power supply apparatus. In particular, the present invention relates to power supply controller apparatus for detecting whether or not each contactor is welded using an AC signal.
2. Description of the Related Art
In recent years, in electric vehicles such as pure electric vehicles (PEVs), hybrid electric vehicles (HEVs) or the like, the power supply apparatus using secondary batteries such as nickel-metal hydride batteries with high-energy density (hereinafter referred as to “nickel-hydrogen batteries”) or the like has been used as a power source for use in a motor or a drive source for various types of loads. The power supply apparatus for use in an electric vehicle requires a total voltage of 100V to 350V. The output voltage of a single battery (a cell), which is the minimum unit of a battery assembly constituting the power supply apparatus, is approximately 1.2V. Hence, in usual, a plurality of cells (e.g. 100 cells) are connected in series to each other to obtain a desired total voltage.
Contactors (relays) are provided between the power supply apparatus and the motor to connect and disconnect the power source. For example, in PEVs, when a vehicle driver turns on an ignition key to start supply of the power, the contactors are controlled to be in conductive state to connect the power supply apparatus to the motor, and then the motor is driven to rotate. When the vehicle driver turns off the ignition key, the contactors are controlled to be in non-conductive state to disconnect the power supply apparatus from the motor, and then the motor is stopped.
Generally speaking in PEVs and HEVs, a capacitor for smoothing the output voltage is provided in order to stably supply a DC voltage to the motor. As described above, the total voltage of the power supply apparatus is extremely high. Hence, in the case that the contactors are controlled to be in conductive state when the electrical charge of the capacitor is almost empty, a large-current instantaneously flows between the conducting contacts of the contactor. By repeating this, the contacts are heated, melted, and then pressured, and as a result, the contacts might be welded each other. The welding of the contactors causes malfunction of the entire apparatus. A power supply controller apparatus of a prior art for detecting welding of contactors is disclosed in the Japanese patent laid-open publication No. 2000-134707.
Referring to FIGS. 14 and 15, the power supply controller apparatus of the prior art will be described.
FIG. 14 is a block diagram showing a configuration of an electric vehicle having the power supply controller apparatus of the prior art. In FIG. 14, a battery assembly 1 has such a configuration that a plurality of single batteries are connected in series to each other. The positive terminal of the battery assembly 1 is connected to a first contactor 2. The negative terminal of the battery assembly 1 is connected to a second contactor 3. A third contactor 4 and the current-limiting resistance 5 form a series circuit. The series circuit is connected in parallel to the first contactor 2.
Each of the first contactor 2, the second contactor 3, and the third contactor 4 includes a moving contact and a fixed contact. Each contactor switches over between conductive state (ON state) and non-conductive state (OFF state) of the contacts under control of a controller 8.
An inverter 32 is constituted by a plurality of transistors and a plurality of diodes. The inverter 32 sequentially applies the power supply voltages to respective phases of the motor 34 to drive the motor 34. A capacitor 6 is a smoothing capacitor for stably supplying a DC voltage to the inverter 32. A voltage detector 7 detects a voltage Vinv applied between both ends of the inverter 32 (hereinafter referred as to “an inverter voltage Vinv”).
The controller 8 receives an input signal from an operation input part 36 and controls switching over of each contactor between conductive state and non-conductive state thereof. The controller 8 reads out the inverter voltage Vinv from the voltage detector 7 and detects welding of each contactor depending on the control state of each contactor. The controller 8 outputs display information for notifying the operator of incidence of the welding to a display output part 38, to display the same information thereon when the controller 8 determines that any contactor is welded.
The operation input part 36 is, for example, an ignition key that is operated by an operator such as a driver of the electric vehicle or the like. The display output part 38 is, for example, a lighting apparatus such as LEDs or the like. In the case that the controller 8 determines that any contactor is welded, the display output part 38 is made to be lighted responsive to an instruction from the controller 8 to notify the operator of incidence of the welding.
Referring to FIG. 15, a process for detecting welding of the contactors in the power supply controller apparatus of the prior art will be described. FIG. 15 is a timing chart showing control signals 52, 53 and 54 from the controller 8 to the first contactor 2, the second contactor 3, and the third contactor 4, respectively, regarding a typical operation in a power supply controller apparatus for use in an electric vehicle.
At the timing TO, the operator turns on the ignition key of the operation input part 36 to supply the power. At this timing, since the contactors 2, 3 and 4 are controlled to be turned off. Therefore, if no contactors are welded, the inverter voltage Vinv detected by the voltage detector 7 is almost zero during the time interval between the timings TO and T1. That is, if the inverter voltage Vinv detected by the voltage detector 7 increases for this time interval, it shows that at least one of the first contactor 2 and the third contactor 4, and the second contactor 3 are welded.
At the timing T1, the third contactor 4 is controlled to be turned on. If no contactors are welded, the inverter voltage Vinv detected by the voltage detector 7 is almost zero during the time interval between the timings T1 and T2. That is, if the inverter voltage Vinv detected by the voltage detector 7 increases for this time interval, it shows that the second contactor 3 is welded.
At the timing T2, the third contactor 4 is controlled to be turned off before the second contactor 3 is controlled to be turned on at the timing T3. If no contactors are welded, the inverter voltage Vinv detected by the voltage detector 7 is almost zero during the time interval between the timings T3 and T4. That is, if the inverter voltage Vinv detected by the voltage detector 7 increases for this time interval, it shows that at least one of the first contactor 2 and the third contactor 4 is welded.
At the timing T4, with keeping the second contactor 3 be turned on, the third contactor 4 is controlled to be turned on again. The precharge of the capacitor 6 is started. At this timing, since the current-limiting resistance 5 is provided, no large-current flows between the contacts of the third contactor 4. At the timing T5 when the capacitor 6 is fully charged, the first contactor 2 is controlled to be turned on, and then the voltage of the battery assembly 1 is applied to the inverter 32 so as to start driving of the motor 34. At the timing T6, the third contactor 4 is controlled to be turned off.
Further, at the timing T7, the operator turns off the ignition key. At the same timing, the first contactor 2 is controlled to be turned off to stop driving of the motor 34. If no contactors are welded, the inverter voltage Vinv detected by the voltage detector 7 decreases during the time interval between the timings T7 and T8. That is, if the inverter voltage Vinv detected by the voltage detector 7 does not decrease and is kept be nearly equal to the voltage between both ends of the battery assembly 1 for this time interval, it shows that the first contactor 2 is welded. At the timing T8, the second contactor 3 is controlled to be turned off. As described above, the power supply controller apparatus of the prior art detects which contactor is welded.
However, as is understood from FIG. 15, in the power supply controller apparatus of the prior art, the controller 8 is required to keep the third contactor 3 be turned on during the time interval between the timings T1 and T2 for the purpose of detecting welding of the second contactor 3. This leads to that the number of time of switching of the third contactor 4 is twice as much as that in the case of no welding detection. This causes reduction of the service life of the third contactor 4, by extension, causes reduction of the service life of the entire electric vehicle.
Additionally, in the case that the inverter voltage Vinv is measured, necessary circuits and wire harnesses for measuring the inverter voltage Vinv cost high. Furthermore, in the case that the value of the inverter voltage Vinv is read out from the other electronic control unit (ECU) that controls the inverter, it takes time to communicate with each other. It is disadvantageous to shorten the time required for welding detection.
Additionally, for the purpose of detecting welding of the first contactor 2, electric charge in the smoothing capacitor (the capacitor 6 of FIG. 14) is required to be discharged for security, and therefore, it takes time to wait for discharging the capacitor during the time interval between the timings T7 and T8 of FIG. 15 (usually more than 10 minutes). An additional load for discharging the electric charge in short time increases the number of components, and as a result, the power supply controller apparatus becomes more expensive.